This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 11(1999)-267039 filed on Sep. 21, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a vehicle brake system. More particularly, the present invention pertains to a brake control device for a vehicle provided with pressurization mechanisms for pressurizing brake fluid supplied to the wheel brakes in response to the driver""s operation and independently of the driver""s operation.
A known vehicle brake control device is disclosed in Japanese Patent Laid-Open Publication No. 60(1985)-78849. This brake control device includes a vacuum booster having a solenoid, a depressing force sensor for detecting the depressing force of the brake pedal, a deceleration sensor for detecting the deceleration of the vehicle, and a control device. The solenoid is disposed in a housing of the vacuum booster and operates independently from the brake operation member. The depressing force sensor is disposed on the input axis of the vacuum booster and detects the depressing force as an operating force of the brake pedal. In this device, even though the condition of the vehicle such as the carrying weight is changed, if the depressing force is constant, the solenoid is controlled by the control device so that the predetermined target deceleration of the vehicle is always obtained. In other words, the solenoid is controlled by the control device under feedback control. As a result, the relationship between the depressing force of the brake pedal and the deceleration of the vehicle is maintained constant.
With this known brake control device, the depressing force sensor for correctly detecting the depressing force of the brake pedal is indispensable for feedback control. Because the depressing force sensor is expensive due to its rather complicated structure, the manufacturing cost of the brake control device is increased.
Moreover, in this known brake control device, a variety of vehicle conditions such as the carrying weight cause an increase of the operating force of the pedal.
In light of the foregoing, a need exists for a vehicle brake control device which overcomes the above drawbacks.
It would thus be desirable to provide a vehicle brake control device which can reliably produce a braking force in response to changes in the vehicle condition without using a depressing force sensor and feedback control.
The brake control device of the present invention includes a pressurization device having a first pressurization mechanism for pressurizing brake fluid supplied to wheel brakes in response to the driver""s operation and a second pressurization mechanism for pressurizing the brake fluid supplied to the wheel brakes independently of the driver""s operation, a first detecting mechanism for detecting the displacement of an input member of the pressurization device or an output pressure of the pressurization device; a second detecting mechanism for detecting the condition of the vehicle, and a control device for memorizing relationships between a driving signal of the second pressurization mechanism and the displacement of the input member or relationships between a driving signal of the second pressurization mechanism and the output pressure of the pressurization device as control maps corresponding to variations in the condition of the vehicle. The control device also controls the driving signal of the second pressurization mechanism on the basis of the control map in response to the value detected by the first detecting mechanism and the condition of the vehicle detected by the second detecting mechanism.
The control device selects a control map corresponding to the condition of the vehicle detected by the second detecting mechanism and controls the driving signal of the second pressurization mechanism on the basis of the selected control map in response to the value detected by the first detecting mechanism. Therefore, the output of the pressurization device can be controlled variably without using a depressing force sensor and feedback control in response to the condition of the vehicle.
It is preferable that the control device output a predetermined driving signal to the second pressurization mechanism when the control device judges that the brake is not operated by the driver, with the control device correcting the target relationship according to the detected value by the first detecting mechanism at this time. The control device can thus correctly control the second pressurization mechanism even if leakage of brake fluid, wear of a brake pad or wear of a mechanical portion occurs.
It is preferable that the pressure device include a vacuum brake booster with an actuator. In this way, the input-output ratio of the pressurization device having the vacuum brake booster can be changed by driving the actuator as the second pressurization mechanism.
The second pressurization mechanism is preferably comprised of a modulator which draws in brake fluid from a master cylinder and pressurizes the wheel brakes. The input-output ratio of the pressurization device can thus be changed by driving the modulator as the second pressurization mechanism.